Obesity rates in American youth have increased dramatically in recent decades. Since obese adolescents are very likely to become obese adults, it is important that the factors that underlie the development of obesity in youth be identified, understood, and targeted in future public health interventions. Numerous authorities have suggested that increasing rates of obesity are, at least in part, due to declining physical activity and increasing participation in sedentary behaviors. It is known that physical activity levels are lower in girls than boys and that physical activity declines with increasing age during adolescence;however, the roles of physical activity and sedentary behavior in preventing adolescent obesity are still not well understood. The Trial of Activity for Adolescent Girls (TAAG) was a multi-center, randomized, controlled field trial that examined the effects of a school plus community intervention on physical activity in middle school girls. Accelerometry was used to objectively measure physical activity in a sample that was diverse in terms of geography, race/ethnicity, socioeconomic status, body composition, physical activity, and other health behaviors. Body composition, types and contexts of physical activity, and psychosocial correlates of physical activity were also measured. The proposed investigation, Longitudinal Assessments in TAAG (LA- TAAG), will track TAAG participants from Louisiana who were measured in 8th grade in spring 2006 and will be re-measured in spring 2009 to observe changes in body composition and levels of physical activity. Further, personal, school, and built environmental factors that may influence physical activity levels and/or weight status will be studied using multi-level models. Finally, we will examine whether persistent stress and anxiety resulting from a disruptive event, such as Hurricane Katrina, could negatively influence physical activity and/or weight status. Project Narrative: Obesity rates in American youth are increasing. More information is needed on how changes in objectively measured physical activity are related to changes in body mass index and percent body fat during adolescence. We will also explore the influence of personal, school and environmental factors, including persistent stress and anxiety that may have resulted from Hurricane Katrina, on these relationships.